This invention relates to air curtain-type refrigerated display cabinets, and more particularly to a novel air defrost refrigerated display cabinet.
Multiple air curtain refrigerated display cases or cabinets have, within the past 15 to 20 years, gained wide acceptance in the food market industry. Such cabinets provide advantages in the storage and display of refrigerated or frozen foods and the like. The cabinets generally employ two or three air curtains traversing the open front of the display case; the innermost air curtain and the adjacent one are normally recirculated around the cabinet through conduits provided therein. The innermost air curtain is normally the coldest, the second one being somewhat warmer, and the third outermost one, if such is provided, being basically an ambient temperature curtain to reinforce the jet inertia of the two innermost curtains. Refrigeration means, normally in the form of one or more evaporator coil units, is located in the innermost passage for cooling the air flowing past. Periodically during operation, this innermost passage and its refrigeration means must be defrosted to remove accumulated frost on the coil collected from the cooled air and tending to impede the operation of the equipment.
Three principal types of defrosting means may be employed on commercial units. The most common type utilizes electric heaters adjacent the coils of the refrigeration means whereby high voltage electrical heaters warm the recirculating air curtain when the refrigeration operation is temporarily halted. The warmer air passing over the refrigeration coils melts snow or frost accumulated on the coils. A second type of defrosting means, far less common because of its complexity, employs heated gas which is circulated through the refrigeration coils during the defrost cycle. Hot gas defrost requires complicated valving structures to selectively channel refrigerant through the coils during the cooling cycle and hot gas through the same coils during the defrost cycle.
A third type of defrosting means, with which this invention is concerned, employs ambient air that is substantially warmer than the refrigerated air circulating through the system, to warm the coils during the defrost cycle and thus melt accumulations of snow or frost. Air defrost systems per se are not new, as evidenced by Beckwith et al. U.S. Pat. Nos. 3,403,525 issued Oct. 1, 1968, 3,850,003, issued Apr. 5, 1974, and 3,937,033 issued Feb. 10, 1976. In known systems, as exemplified by the Beckwith patents, specific fans are turned on during a defrost cycle to pull air out of the primary refrigerated air band path, exhausting this air to the atmosphere while at the same time drawing ambient air into the refrigerated band conduit. During the defrost cycle, in the known systems, the air curtain across the open front of the display case dissipates completely, thereby permitting moisture laden ambient air to infiltrate the display section during the defrost cycle. This has a tendency to cause an increase in frost build-up to occur in the display area during the refrigeration cycle.
Another Beckwith patent, U.S. Pat. No. 3,082,612, issued Mar. 26, 1963, discloses an air curtain refrigerated cabinet and defrosting means for defrosting the refrigeration coils without the need for completely shutting down the refrigeration cabinet. The cabinet utilizes the existing main air passage circulation fan for drawing in ambient air from a passage through ports located in the lower front portion of the apparatus. The ports are closed during normal operation by shutter plates. The ambient air drawn in through these passages is discharged from the main refrigeration band at a point beyond the refrigeration coils through a further passage via ports located in the rear of the apparatus. The Beckwith et al. '003 patent indicates that the concepts described in U.S. Pat. Nos. 3,082,612 and 3,403,525 did not prove practical and therefore were not commercially feasible.
The present invention comprises an arrangement whereby pivoting a fan panel opens doors to the atmosphere to place the door and the fan panel in such a position that room air may be drawn directly, by already existing fans, into the second air band of the refrigerator. This reverses the normal air flow in the second air band, thereby taking the ambient air directly into a discharge relationship at the lower front opening of the refrigerator. One purpose of this is to draw room air, with its greater heat content, into the refrigerator to be discharged in such a position that it may be drawn directly into the lower opening which supplies the air from the main refrigeration passages and components.
In an alternative arrangement, reversible fans are provided in place of the pivotable fan panel to achieve a similar result.
In addition, there is a normal arrangement between the main refrigeration passages and the second band passages whereby, during defrost, air is taken from the second band and directed by an appropriate scoop into the main refrigeration air passages. It is the purpose of this to provide, by stationary parts, a means to cause the ambient air in the second band, during defrost, to be turned into the refrigeration air passages. There is a normal tendancy of the air from the second band to turn from its discharge to be drawn into the refrigeration band with the purpose of defrosting it, essentially to accomplish the total utilization of the available ambient air for the purpose of defrosting.
In an alternative arrangement, a movable member is provided to shunt air from the second band passage into the main air passage during a defrost cycle.
It is an object of the present invention to overcome disadvantages associated with known air defrost systems.
More particularly, it is an object of this invention to circulate ambient air through the primary and secondary air band conduits during a defrost cycle.
It is a further object of the invention to maintain an air curtain across the open front of the display case during the defrost cycle to prevent infiltration of ambient air into the display area.
It is a further object of the invention to provide a means whereby ambient air is drawn directly into the secondary air band conduit during the defrost cycle and the air flow through the secondary air band is reversed during the defrost cycle as compared to the refrigeration cycle.
It is a further object of the invention to maintain the air flow in the primary air band conduit in the same direction during both the refrigeration and defrost cycles.
It is a further object of the invention to provide means for drawing ambient air from the secondary air band conduit into the primary air band conduit during the defrost cycle while preventing such transfer during the refrigeration cycle.